This invention relates to a method and apparatus for position and orientation measurement using a magnetic field and retransmission. There has long been a need for a position and orientation measuring system including a passive sensor unconnected to the computing portion of the system, with the system being capable of tracking a plurality of objects and including great simplicity. In the prior art, this combination of features has been found to be lacking as should become clear from the detailed discussion of the prior art known to applicant, as follows:
U.S. Pat. No. 3,868,565 to Kuipers discloses a system which detects the position and orientation of an object in two dimensions (FIGS. 9-10) or three dimensions (FIG. 11). For example, (FIG. 11), the object has affixed thereto mutually orthogonal magnetic field sensing coils related to magnetic field generating coils. Signals are induced in the sensing coils dependent upon their position and orientation to thereby determine the object's position and orientation. This system is quite different from the systems disclosed herein in that there is no separation of the source coils and the sensor coils, information transformation between the source and the sensor is necessary, no retransmission of the magnetic field is contemplated, the sensor is not passive, the patented invention may only detect one object at a time and there is no means for compensation for non-orthogonality of coils or for metallic scatters.
U.S. Pat. No. 4,054,881 to Raab discloses three mutually-orthogonal radiating antennas each of which transmits electromagnetic radiation to three mutually orthogonal receiving antennas. The receiving antennas measure the radiated signals and produce nine parameters which enable calculations of the position and orientation of the receiving antennas with respect to the transmitting antennas. This patented invention is quite different from the inventions disclosed herein for many reasons including: there is no retransmission of the magnetic fields utilized therein, the transmitting and receiving antennas are integrally connected in the system and the sensor is not passive; further, there is no means for compensation for non-orthogonality of coils or for metallic scatters.
U.S. Pat. No. 4,119,908 to Cosman, et al., discloses a means for locating a pole box buried underground which includes the use of a passive marker including a circuit resonant at a particular frequency. A transmitter is utilized to generate the particular frequency of resonance of the passive marker to thereby enable detection thereof. There are several differences from this invention and the inventions disclosed herein including the fact that the transmitter is moved while the passive marker remains stationary just opposite to the structure and operation of the present invention, the passive marker's resonant circuit merely changes the magnetic pattern transmitted from the transmitter along the pipe and as such no real retransmission in the sense with which retransmission is contemplated in the present invention is used and, further, any measurements contemplated by the patented invention are only in two dimensions whereas with the present invention three-dimensional, as well as three additional degrees of freedom including pitch, roll, and yaw, are measured.
U.S. Pat. No. 4,281,321 to Narlow, et al., discloses a system which determines the presence of a surveillance tag attached to merchandise. The system includes a mat which forms a capacitive coupling with a pedestrian who steps thereon. If this pedestrian is carrying merchandise which includes a surveillance tag attached thereto indicative of the potential theft of the merchandise, the surveillance tag is sensed by the system. This invention is vastly different from the inventions disclosed herein since it merely detects the presence of a surveillance tag and not the precise position and orientation thereof. Further, there is no use in the patented invention of mutually orthogonal coils in either the transmitter or sensor and, further, the system operates with a very high frequency well above the low frequency magnetic near-field utilized by the present invention.
U.S. Pat. No. 4,303,910 to McCann discloses a system for monitoring the position of a retransmitter attached to a target within a work area. A transmitter or transmitters transmit a signal into the work area which is retransmitted back to a receiver. The receiver determines the position of the retransmitter by interpreting the received signal. This invention is different from the inventions disclosed herein basically because no position or orientation measurements are made and further for the reasons set forth with regard to the above-discussed U.S. Pat. No. 4,281,321.
U.S. Pat. No. 4,308,530 to Kip, et al., discloses a system which includes a wafer with a resonance circuit including a coil capacitor and diode. A transmitter transmits signals at two frequencies and a receiver receives signals retransmitted by the wafer to determine when the wafer is located in an unauthorized location while attached to an object being monitored thereby. This system is a theft-detection system similar in nature to the above-discussed U.S. Pat. No. 4,281,321 and 4,303,910. The system is only able to detect the presence of the receptor-reradiator in a surveillance area and does not detect the position or orientation thereof.
U.S. Pat. No. 4,356,477 to Vandebult discloses a resonant tag circuit responsive to at least one frequency of electromagnetic radiation. A transmitter transmits a signal at a frequency at which the circuits in the tag resonate, with the resonant signal being detected by a receiver for a variety of purposes. Again, this is a theft-detection system similar in nature to the above-discussed U.S. Pat. Nos. 4,281,321; 4,303,910 and 4,308,530 and is distinct from the teachings of the present invention for the same reasons as noted hereinabove.
The following prior art U.S. patents are also known to applicant and are believed to be of only general interest to the teachings of the present invention: Nos. 3,457,502; 3,644,825; 4,041,285; 4,160,204 and 4,314,251.